Tag selector loses XBL bindings ("'tagSelector.focusTextbox();' is not a function")

[kkraus]

A user reports that the tag selector feature is not available in her Zotero installation:

Checked the error log. The error reports that the statement, "tagSelector.focusTextbox();" (which it highlights in the following function) is "not a function"

function toggleTagSelector(){

var zoteroPane = document.getElementById('zotero-pane');
var tagSelector = document.getElementById('zotero-tag-selector');

var showing = tagSelector.getAttribute('collapsed') == 'true';
tagSelector.setAttribute('collapsed', !showing);
this.updateTagSelectorSize();

If showing, set scope to items in current view
and focus filter textbox
if (showing) {

_setTagScope();
tagSelector.focusTextbox();

}
If hiding, clear selection
else {

tagSelector.uninit();

}

I can't tell you much more than this because it just has never worked on my laptop and I only discovered it existed when I was using Zotero on my desktop where it works perfectly well.
Zotero is installed and updated on both machines in the same way with the same version of Firefox running on both.

[dstillman]

As I mentioned to Kari, I can't think of any way that this could happen. We'll check back in with the user after the next beta.

[dstillman]

This happened to me--I was able to fix it by clearing prefs.js, but I accidentally deleted the copy of the file, so I wasn't able to investigate further. Can diagnose if it happens again (or someone can send me a copy of prefs.js when this occurs).

[dstillman]

I can reproduce this by enabling nglayout.debug.disable_xul_cache. Checking with user to see if that was the source of the problem.

[dstillman]

I'm guessing user installed Extension Developer's Extension and enabled developer prefs, including disable_xul_cache.